For wet tires for competition, a compound that achieves high wet grip performance, period of time required to exhibit the grip performance, stiffness, durability, and wear resistance at high levels has been demanded.
To enhance the grip performance, techniques that use styrene-butadiene copolymer rubber (SBR) having a high glass transition temperature (Tg) (e.g. see Japanese Unexamined Patent Application Publication No. H10-204216A) and techniques that blend a large amount of silica as a reinforcing filler have been used.
However, when an SBR having a high Tg is used, there are problems in grip performance particularly at low temperatures and problems in that longer period of time is required to exhibit the grip performance. Furthermore, in the techniques to blend a large amount of silica, problems exist in that the silanol groups present on the surface of the silica particles aggregate by forming hydrogen bonding, thereby making the Mooney viscosity of the rubber composition higher during kneading, and thus processability is deteriorated and wear resistance is also deteriorated.